During the last couple of decades, much work has been done to try to determine earth's average temperature over a long period of time. One of the ways this is done is by drilling ice samples in Greenland and determining from the layers of ice (much like tree rings) what gases are present and what the average temperature was that year.

Unfortunately, this record over Greenland appears to give valid readings only up until the last inter-glacial period. Luckily enough, the drill records for the Antarctic have recently revealed records over the last 400 thousand years.

Temperature variations over the last
400.000 years showing 4 inter-glacial periods

Consider this chart of temperatures over a 400 thousand year time period recently gained from ice cores in the Antarctic. Please read from left to right. It starts at current temperatures and goes back in time. It shows the recent spike that marks the end of the last glacial period. Notice the cold periods extend for about 100.000 years and there are 4 warm spikes approx. every 100.000 years that last for an average of 10.000 years. These correspond with readings taken in Greenland over the period of time that Greenland can be measured and are viewed as reflective of overall climate on Earth.

Any description of global warming will have to address the temperature's cyclical nature over the last 400.000 years.

Extent of Glaciers

Ice coverage of the northern hemispere 18.000 years
before present compared to modern day

left: earth 18.000 years ago as viewed from the north pole ||||||||||||||| right: earh today as viewed from the North Pole
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Consider these pictures showing ice levels (white and light blue) towards the end of the last glacial period (about 18k years ago) compared to ice levels now (an inter-glacial period). The world was very different, with the ice covering New York, Toronto, Edmonton, Calgary, ... in the 1-2 kilometer range. The sea level was some 100 meters lower than present and the shore lines were closer to what is called the continental shelf, rather than current ocean shore lines. Notice also the land bridge between Alaska and Russia (light green) that facilitated the movement of humans into the Americas from Asia during the last glacial period.

Any description of global warming will have to address the issue of the last 10k years that shows a dramatic reduction in ice buildup over Canada and northern Europe.

During the period of polar ice cap melting, consider the Atlantic Ocean. Most of the cold, fresh water created by the melting flows out through the North Atlantic. Very little comes out to the Pacific just because of how the land is. Remember the movie Red October, where submarines use the rush of cold water deep in the ocean between Iceland and England to travel quickly into the mid Atlantic Ocean. This rush of deep cold fresh water causes a current that forces the surface warmer water to flow north towards Europe and estabilishes most of the overall ocean currents. The warm weather in northern Europe and eastern Canada contributes to and intensifies the melting of the ice cap, which in turn intensifies the warmer northern weather, thus causing more melting, more flow of water and warmer weather yet.

This cycle clearly cannot continue forever. At some point enough of the polar ice cap has melted so that there is no longer such a large net flow of cold water out of the Arctic. At this point the northern flow of warm water on the surface and the warm air flowing into Northern Europe will be reduced. Instead of melting, the Arctic will again start to build up ice. The slow 100k glacial period will start and the buildup of ice will continue over the 100k years since there is no more north Atlantic current to melt the ice. The feedback loop of melting causing warm weather is now replaced with freezing of the ice cap causing cooler weather. The ice cannot build up forever, as the earth absorbs too much energy from the sun to completely freeze up. So at some point, the build up of ice is enough that it starts to melt even though the north Atlantic is not warming it. At that point, the north Atlantic will again start the warming feedback loop and the cycle of dramatic warming (10k years) followed by slow freezeup (100k years) will continue.

Remember too, although the buildup of ice takes a long time, the actual temperature changes in a particular place caused by the flow of the ocean occur on a much smaller time frame. The temperature charts show differences ranging from 2 degrees to 10 degrees celsius occuring over a relatively short time frame (ie. decades). The principle change will come in the flow of the Atlantic Ocean and the related weather changes caused by no more gulf stream affecting the weather in Eastern Canada, the Eastern US and Northern Europe.

Conclusions

The earth has a natural warming and cooling cycle that lasts just over 100 thousand years. The cycle goes from virtually no ice in the arctic, to substantial buildup of ice in the arctic. The complete melting of the polar ice cap is what triggers the next round of cooling. The natural flow of the Atlantic Ocean is what sustains the warming and cooling cycles.

The sea level would rise another 6.5 meters if most of the ice on Greenland melts (as it did in the last and every other interglacial period). Also remember that the melting of the ice shield over North American and Europe over the last 10k years has raised sea levels by an estimated 120 meters. How long before all of the Greenland ice melts and sea levels rise another 6 meters? 500 years? 200 years? What will happen after it melts? Will the Atlantic ocean current reverse causing considerably cooler temperatures for a long time in places like Northern Europe, Toronto and New York?

There exists a clear record of what has happened in the past. Will it happen again? We need to know.